1. Field of Invention
The present invention relates to valve stem seal assemblies for use in internal combustion engines, and more particularly to sealing media applied to bottom flange portions of such seal assemblies.
2. Description of the Prior Art
Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves include integral elongated stems extending away from the engine cylinder heads, the ends of the stems interacting with rotating cams for cyclic repeated opening and closure of the valves during the combustion cycle. The valve stems thus move reciprocally to and from the cylinder head, and so-called valve stem seal assemblies, also variously called oil seal assemblies, are used to seal against leakage of oil through a clearance path between each annular engine valve guide and an associated valve stem supported for reciprocal motion within that particular guide. Obviously, in order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must exist between the valve guide and the moving stem.
Thus as is well known, the intake ports of a combustion chamber are opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and rotary with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of the same construction, and include stems integrally affixed to the valves.
In the typical engine, an oil seal assembly is fitted over each valve stem, each assembly being frictionally mounted over an associated valve guide to assure its securement within the engine. Typically each oil assembly has two primary parts; 1) an elastomeric oil seal positioned at one end to control leakage of oil between the valve stem and guide as noted, and 2) a structural cylindrical part called a retainer which is mounted atop of and frictionally secured to the valve guide. In some cases, the retainer has a so-called bottom flange that extends from the top of the valve guide downwardly to the cylinder head deck. As those skilled in the art will appreciate, the cylinder head deck provides support for the bottom flange on which the valve return springs bear. It has long been felt that the spring pressure against the bottom flange has been sufficient to deter or otherwise avoid the usually minor leakages of oil between the valve guide and the cylinder head deck. Thus, while there have been significant advancements in the art with respect to the elastomeric oil seals which engage valve stems, little emphasis has been placed on control of oil leakage between the normally press-fit interface between the valve guide and the engine cylinder head.
The present invention addresses the latter issue.
The present invention is an improved system for sealing between the valve guide and the cylinder head of an internal combustion engine. A valve stem seal assembly includes a metallic retainer that incorporates a bottom flange for supporting return springs of a reciprocating valve and stem. The bottom flange contains a bonded coating, lip, ring, or other sealing media for the purpose of sealing against leakage of oil between a valve guide positioned in the engine mounting surface, or cylinder head deck. Thus, the inventive sealing media is directed to the interface between valve guide and cylinder head, wherein oil tends to flow down a path between the normally press-fit interface of the noted parts.
The invention contemplates several methods of achieving the so-called bottom flange seal, including screen printing or pad printing of circular elastomeric sealing rings, screen printing or pad printing of an elastomeric sealing grid, rolling an elastomeric sealing coating, or bonding an elastomeric sealing lip to an inside (radially innermost) edge of the annular bottom flange.
The invention thus complements the traditional annular elastomeric seal, which is adapted only to control oil leakage between the valve stem and the valve guide.